Chemokine-driven inflammation plays an important role in the reparative response following myocardial infarction and is critically involved in the pathogenesis of adverse remodeling. Differential expression of chemokine receptors by monocyte and lymphocyte subsets governs their trafficking in the infarcted myocardium resulting in infiltration with subpopulations that exhibit distinct functional properties. We propose that beyond their involvement in initiation and activation of the post-infarction inflammatory reaction, chemokine-mediated interactions also play an important role in suppression of inflammation through recruitment of leukocyte subsets with inhibitory properties. Our studies suggest that signaling through the CC chemokine receptor 5 (CCR5) mediates recruitment of suppressive monocyte subsets and regulatory T cells (Tregs), a CD4+ T lymphocyte subpopulation with an essential role in regulation of immune responses. Accordingly, the objective of the current proposal is to investigate the role of Tregs and inhibitory monocyte subpopulations in regulation of post-infarction inflammation, to study the molecular signals responsible for their protective effects, and to explore the role of chemokine signaling in their recruitment in the infarcted myocardium. These concepts will be examined in three specific aims: Specific aim 1: to investigate the role of monocyte subsets with anti-inflammatory properties in controlling the post-infarction inflammatory response. Specific aim 2: to study the involvement of Tregs in inhibition of inflammatory injury, in prevention of excessive matrix degradation and in protection from the development of adverse remodeling following myocardial infarction. Specific aim 3: to investigate chemokine/chemokine receptor interactions responsible for recruitment of Tregs and effector T cells in the infarcted myocardium. Chemokine-mediated suppression of inflammation through recruitment of regulatory mononuclear cell subpopulations appears to play an essential role in cardiac repair and protects from the development of adverse remodeling. Understanding the effects of inhibitory monocytes and Tregs may identify novel therapeutic targets for pharmacologic interventions and cell therapy in patients with myocardial infarction.